Re: [Qemu-devel] [PATCH 2/2] open ptys in non-blocking mode.

[Kevin Wolf <kwolf@suse.de>]

[Crossposting to xen-devel]

Ian, we need something like this for qemu-xen (or ioemu-remote or
whatever it's called now). Currently you must attach to the console of a
domain, otherwise it won't boot up and keep hanging in a blocking write
because the buffer is full.

The old ioemu had a hack in unix_write (doing a select before the write)
which you didn't merge into qemu-xen. In fact, I noticed that you even
removed that function entirely and I'm wondering why.

Kevin

Gerd Hoffmann schrieb:
> Otherwise qemu will hang in case nobody connects to the pty and the
> guests prints enougth messages to fill up the buffer (which is 4k
> in linux).
> 
> Downside is that data may get lost in case the reader is too slow.
> 
> Ideally we could detect whenever someone is connected to the other end
> of the pseudo tty and write data only in connected mode (like it is done
> for tcp/telnet).  I'm not aware of any way to accomplish that though.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  vl.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/vl.c b/vl.c
> index 587b91c..adc8f5f 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2468,6 +2468,7 @@ static CharDriverState *qemu_chr_open_pty(void)
>      /* Set raw attributes on the pty. */
>      cfmakeraw(&tty);
>      tcsetattr(slave_fd, TCSAFLUSH, &tty);
> +    socket_set_nonblock(master_fd);
>  
>      fprintf(stderr, "char device redirected to %s\n", ptsname(master_fd));
>      return qemu_chr_open_fd(master_fd, master_fd);